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ELEN602 Lecture 3 Review of last lecture –layering, IP architecture Data Transmission

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Receiver Communication channel Transmitter Abstract View of Data Transmission Communication Channel Properties: -- Bandwidth -- Transmission and Propagation Delay -- Jitter -- Loss/Error rates -- Buffering

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(a) Analog transmission: all details must be reproduced accurately Sent Received e.g digital telephone, CD Audio (b) Digital transmission: only discrete levels need to be reproduced e.g. AM, FM, TV transmission Analog vs. Digital Transmission

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SourceRepeater Destination Repeater Transmission segment A Typical Communication Channel

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Attenuated & distorted signal + noise Equalizer Recovered signal + residual noise Repeater Amp. An Analog Repeater

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Amplifier Equalizer Timing Recovery Decision Circuit. & Signal Regenerator A Digital Repeater

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communication channel d meters 0110101...

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f 0 W A(f)A(f) (a) Lowpass and idealized lowpass channel (b) Maximum pulse transmission rate is 2W pulses/second (Nyquist rate) 0W f A(f)A(f) 1 Channel t t Characteristics of an Idealized Channel

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signal noise signal + noise signal noise signal + noise High SNR Low SNR SNR = Average Signal Power Average Noise Power SNR (dB) = 10 log 10 SNR t t t t t t Impact of Noise on Communication

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Channel t t A in cos 2 ftA out cos (2 ft + (f)) A out A in A(f) = Channel Characterization -Frequency Domain

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f 1 A(f) = 1 1+4 2 f 2 Signal Amplitude Attentuation

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f 0 (f) = tan -1 2 f -45 o -90 o 1/ 2 Signal Phase Modulation

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1 0 0 0 0 0 0 1... t 1 ms A Pulse

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Output of Low-pass Communication Channel

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Channel t 0 t h(t) tdtd Channel Characterization -Time Domain

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t s(t) = sin(2 Wt)/ 2 Wt T T T T T T T Signaling a Pulse with Zero Inter-symbol Interference

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+A+A -A-A 0 T 2T2T 3T3T 4T4T5T5T 111100 Transmitter Filter Comm. Channel Receiver Filter Receiver r(t) Received signal t Digital Baseband Signal and Baseband Tx. System

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(a) 3 separate pulses for sequence 110 (b) Combined signal for sequence 110 t t TTTTTT TTTTTT

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4 signal levels8 signal levels typical noise

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0 2 4 6 8 /2 Signal levels -- Error Probability /2 = A/(M-1) Channel Capacity = W log (1 +SNR)

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101 0 11001 Unipolar NRZ NRZ-Inverted (Differential Encoding) Bipolar Encoding Manchester Encoding Differential Manchester Encoding Polar NRZ

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Coding Methods -Properties Unipolar NRZ - power = A^2/2 Polar NRZ - power = A^2/4 Bipolar encoding reduces the low-frequency spectrum –Timing Recovery is also easier, used in telephones NRZ Inverted -- A transition means 1, no transition is 0 –Errors occur in pairs Ethernet uses Manchester encoding –A transition from + to - is 1, - to + is 0 (in the middle) –Twice the pulse rate of binary coding Differential Manchester encoding -used in Token rings –Every pulse has a transition in the middle –A transition at the beginning is 0, no transition is 1

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f f 2 f 1 f c 0 Figure 3.27

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Informatio n 111100 +1 0 T 2T2T 3T3T 4T4T5T5T 6T6T Amplitude Shift Keying +1 Frequency Shift Keying +1 Phase Shift Keying (a) (b) (c) 0 T 2T2T 3T3T 4T4T5T5T 6T6T 0 T 2T2T 3T3T 4T4T5T5T 6T6T t t t Amplitude, Frequency and Phase Modulation

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111100 (a) Information (d) 2Y i (t) cos(2 f c t) +2A -2A +A -A (c) Modulated Signal Y i (t) 0 T 2T2T 3T3T 4T4T5T5T 6T6T +A -A (b) Baseband Signal X i (t) 0 2T2T 3T3T 6T6T 0 T 2T2T 3T3T 4T4T5T5T 6T6T T 4T4T5T5T t t t

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(a) Modulate cos(2 f c t) by multiplying it by A k for (k-1)T < t <kT: AkAk x cos(2 f c t) Y i (t) = A k cos(2 f c t) (b) Demodulate (recover) A k by multiplying by 2cos(2 f c t) and lowpass filtering: x 2cos(2 f c t) 2A k cos 2 (2 f c t) = A k {1 + cos(2 f c t)} Lowpass Filter with cutoff W Hz X i (t) Y i (t) = A k cos(2 f c t) Modulator and Demodulator

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AkAk x cos(2 f c t) Y i (t) = A k cos(2 f c t) BkBk x sin(2 f c t) Y q (t) = B k sin(2 f c t) +Y(t) Modulate cos(2 f c t) and sin (2 f c t) by multiplying them by A k and B k respectively for (k-1)T < t <kT: QAM Modulator

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Y(t) x 2cos(2 f c t) 2cos 2 (2 f c t)+2B k cos(2 f c t)sin(2 f c t) = A k {1 + cos(4 f c t)}+B k {0 + sin(4 f c t)} Lowpass Filter with cutoff W/2 Hz AkAk x 2sin(2 f c t) 2B k sin 2 (2 f c t)+2A k cos(2 f c t)sin(2 f c t) = B k {1 - cos(4 f c t)}+A k {0 + sin(4 f c t)} Lowpass Filter with cutoff W/2 Hz BkBk QAM Demodulator

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AkAk BkBk 16 “levels”/ pulse 4 bits / pulse 4W bits per second AkAk BkBk 4 “levels”/ pulse 2 bits / pulse 2W bits per second 2-D signal Signal Constellations

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AkAk BkBk 4 “levels”/ pulse 2 bits / pulse 2W bits per second AkAk BkBk 16 “levels”/ pulse 4 bits / pulse 4W bits per second Other Signal Constellations

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10 2 10 4 10 6 10 810 10 12 10 14 10 16 10 18 10 20 10 22 10 24 Frequency (Hz) Wavelength (meters) 10 6 10 4 10 2 1010 -2 10 -4 10 -6 10 -8 10 -10 10 -12 10 -14 power & telephone broadcast radio microwave radio infrared light visible light ultraviolet light x rays gamma rays Electromagnetic Spectrum

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Attenuation (dB/mi) f (kHz) 19 gauge 22 gauge 24 gauge 26 gauge 6 12 3 9 15 18 21 24 27 30 110 1001000 Figure 3.37 Twisted Pair - Attentuation vs. Frequency

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Center conductor Dielectric material Braided outer conductor Outer cover Coaxial Cable

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35 30 10 25 20 5 15 Attenuation (dB/km) 0.010.1 1.0 10100 f (MHz) 2.6/9.5 mm 1.2/4.4 mm 0.7/2.9 mm Coaxial Cable Attentuation vs. Frequency

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Hea d end Unidirectional amplifier Cable TV Distribution Tree

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Hea d end Upstream fiber Downstream fiber Fiber node Coaxial distribution plant Fiber node Bidirectional Split-Band Amplifier Fiber Hybrid Fiber-Coaxial System

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Downstream 54 MHz 500 MHz Upstream Downstream 5 MHz 42 MHz 54 MHz 500 MHz 550 MHz 750 MHz (a) Current allocation (b) Proposed hybrid fiber-coaxial allocation Proposed downstream

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core cladding jacket light cc (a) Geometry of optical fiber (b) Reflection in optical fiber

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(a) Multimode fiber: multiple rays follow different paths (b) Single mode: only direct path propagates in fiber direct path reflected path

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Optical fiber Optical source Modulator Electrical signal Receiver Electrical signal

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10 4 10 6 10 7 10 8 10 910 10 11 10 12 Frequency (Hz) Wavelength (meters) 10 3 10 2 10 1 1 10 -1 10 -2 10 -3 10 5 satellite & terrestrial microwave AM radio FM radio & TV LF MF HF VHF UHF SHF EHF 10 4 Cellular & PCS Wireless cable Figure 3.48

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